When a vehicle is manufactured, the beam direction of its headlamps is adjusted so that the headlamps illuminate the road adhead effectively without dazzling other road users, and as laid down in the Highway Code. In practice, the upper cutoff of a dipped headlamp beam points downwards in such a manner as to reach the ground at a point between 50 and 75 meters ahead of the vehicle.
However, when the vehicle is loaded, or accelerated or decelerated, the trim of the vehicle changes, and consequently the headlamp beam direction relative to the road also changes. The beam cutoff may be raised in which case other road users may be dazzled, or conversely the beam cutoff may be lowered in which case the headlamps do not illuminate far enough ahead.
It has long been the practice for some makes of car to be fitted with hydraulic or electrical devices for both statically and dynamically correcting the beam direction of headlamps. Generally speaking, such devices comprise: two sensors which permanently sense the distances between the vehicle body and the front and the rear wheels respectively of the vehicle; calculating means responsive to said sensors to generate a signal which is a function of the difference between said sensed distances; and an actuator controlled by said signal to point the headlamps in a new direction relative to the vehicle body such that the headlamp beam continues to point in the correct direction relative to the road.
However, such devices are complicated, bulky, and difficult to install. A considerable amount of space must be provided to receive the two sensors, the actuator, and the hydraulic ducts or electrical conductors which interconnect said items. In addition, these items increase vehicle weight and price.
Mention may also be made, by way of background, of published French patent specification No. 1 455 408 in the name of the pesent Applicant. Said French patent teaches a device for correcting the beam direction of vehicle headlamps by servocontrolling said direction as a function of the elevation of the headlamps of oncoming vehicles. The purpose of the correction is to adapt the direction in which the headlamp beams are pointed to the shape of the road (level or sloping up or down, etc.) each time a vehicle comes the other way in order to avoid dazzling the driver of said other vehicle, rather than to attempt compensating for variations in the trim of the vehicle on which the device is mounted.
Preferred embodiments of the present invention remedy the above-mentioned drawbacks by proposing a device for correcting the beam direction of vehicle headlamps, which device is simple in structure and occupies very little space.